Visa is sovereign state home allows condition of discrepancy of foreign citizen or native citizen or the proof of a kind of license that pass territory. Go up in the passport of traveler going abroad namely or imprint in other and effective viatic certificate upper cover the formalities of attach a slip of paper to a document with comments on it, express to allow its come in and go out or pass this nation territory. If a citizen recalls a state journey, emigrant perhaps study abroad, marry etc, besides need hold passport, still must the visa with corresponding hold, the passport is hold person citizenship and identification, visa is sovereign state home allows foreign citizen is native perhaps the permissive proof that citizen discrepancy condition perhaps passes territory. Visa is general attach a slip of paper to a document with comments on it is on the passport, also some attach a slip of paper to a document with comments on it are on the other journey certificate that replaces a passport, some still issues other paper visa. If American immigrant visa is a kind of application form namely, singapore also sends visa of a kind of other paper to the foreigner, but must use at the same time with the passport, just can produce effectiveness. To the foreigner, all be the identity according to applicant is mixed commonly enter a country the purpose grants different entry visa, if travel, visit one's family, emigrant, study abroad, the visa such as the job, limit the resident time after entering a country. Because visa is phyletic different, ask offerred concerned data is different also. Be opposite commonly with short-term and resident the application limitation that is a purpose is less, the time that awaits approval is shorter also. Right with seeking duty is mixed it is a purpose for a long time habitat, application criterion limitation is more, need approved time longer also, this already made the general way of each country. A country did not allow a foreigner termless the obligation that enter a country (except of the person that have pact) , a foreigner also did not ask the government allows one country the right that he enters a country. The foreigner enters a country is conditional limitation. In recent years, as the development that politics of international trade, international concerns, . Of tourism flourishing, the visa regulation of a lot of countries tends simplify. There also is each other rabbit between each country visa or simplify visa formalitiesagreement.